Hydraulic lift truck



March 5, 1935. v A. M. BARRETT HYDRAULIC LIFT TRUCK 4 Sheets-Sheet 1 Filed Dec. 15, 1932 $7 QrZ/zw" M B arreZZ 6 ygw March 5, A M RE HYDRAULIC LIFT TRUCK Filed Dec. 15, 1932 4 Sheets-Sheet 2 A. M. BARRETT HYDRAULIC LIFT TRUCK [Ill-Ill? 4 Sheets-Sheet 4 Filed Dec. 15, 1932 Ill 7 JMMAXZZf March ,5, 1935.

Patented Mar. 5, 1935 HYDRAULIC LIFT TRUCK ArthurM. Barrett, Chicago, Ill., assignor to Barrett-'Cravens Company, Chicago, Ill., a corporation of Illinois Application December 15, 1932, Serial No. 647,388

6 Claims.

This invention relates to lift trucks of the type described in patent to A. M. Barrett, No. 1,416,675, Truck, May 23, 1922.

The purpose of the present improvement is mainly to provide a lifting mechanism with means for automatically varying the ratio or elfective leverage between the operating lever and the lifting frame according to the Weight of the load encountered. A further object of the invention is to provide a multiple piston pump designed for varying displacement of the fluid operated upon for each complete stroke of the piston rod according to the resistance encountered. Thus, with a light load the'pump is operated at full capacity, while with heavier loads the displacement is less, but the input of power per stroke may be the same as for lighter. loads. Still further objects of the invention are to provide improvements in the structural features of hydraulic lift trucks.

The objects of the invention are accomplished by means of a construction as illustrated, in which:-

Figure 1 is a plan view of the improved truck with the draft and pump operating handle partly broken away and the truck shown reduced in length by breaking away a center portion thereof.

Fig. 2 is an enlarged fragmentary View in side elevation showing operating mechanism connected with a draft-handle. I

Fig. 3 is an enlarged fragmentary view partly broken away and in section showing one ofthe cams for actuating the lifting frame.

Fig. 1 is an enlarged detail showing the pump ing cylinder and its pistons and associated operating mechanism in elevation and section as indicated by the section line 4-4 of Fig. 1.

Fig.5 is a detail in transverse section as indicated by the line 5-5 of Fig.1.

Fig. 6 is a longitudinal section taken on the line 6-6 of Fig. l and shows the lift frame releasing valve mechanism.

Fig. 7 is an enlarged sectionaldetail of the valve.

Fig. 8 is a section taken on line 8'8 of Fig. 1 and shows the lift piston.

The improvements upon whichthis application for patent is based are applicable to power operated trucks but for'the purposes of illustration are herein described and illustrated with reference to manually operated trucks of the type which are much in use in factories for inter-department transport of machinery and other products. Such trucks generally consist of a low-wheeled frame structure or chassis upon which is mounted a load carrying platform or frame which may be elevated-or lowered with reference ,to the truck frame. 1 I

In use such trucks are generally positioned beneath the object which is to be lifted and transported. In order to make the structure as compact and low as possible to run under skids, the lifting frame telescopes-With the truck frame, the two being connected together by parallel links which serve to support and guide the lifting frame when the latter is raised or lowered with reference to the truck frame- The draft handle of the truck is generally used to perform the work of lifting, when the handle is oscillated around a horizontal axis in the manner of a pump handle. The loads which are lifted and transported by means of the truck, in some instances, vary so greatly. in'weight that it is found impracticable to have a constant ratio between theoperating lever and the lifting platform. It is important to raise the load as rapidly as possible and it is thereforedesirable to have a mechanism which .will lift a light load upon one or two strokes of the operating handle. In order to suit this mechanism to light an heavy loads the hydraulic pumpoperated therematically changed according to the work to be I performed.

The improved construction also provides an enclosed oil circuit for hydraulic lift mechanisms which does not require stuffing boxes, as the circuit is completely closed below the oil level.

Referring to'the drawings, the wheeled truck frame consists of the side frame elements 1 and 2 connected together by the rear bolster 3 and the front bolster 4. Thefront bolster is the bearing for king pin 5 which carries the front wheel steering structure 6. i The lifting frame includes the longitudinal elements 7 and transverse elements 8. This-frame is connected to the truck frame by the parallel. links 9, the opposite ends of which are pivotally connected with the truck and lifting frames.

When the lifting frame is in its lower position, the side members '7 are at substantially the same level-as side membersl and 2. In Fig. 2 the lifting frame is also shown by broken linesgin its upper position. The lifting frame is shifted from its lower to its upper position by means of cams l0, keyed to a transverse shaft 11, journaled in bearings 12 bolted to the truck frame members 1 and 2. The side members '7 of the lift frame carry rollers 13 which are engaged by the cams 10. A rocking of shaft 11, for the purpose of lifting frame '7, is accomplished by means of a crank 14, Fig. 8. This crank is connected by a pitman 15 with a piston 16 in cylinder 17. This piston 16 is driven-forwardly or to the right, Fig. 8, by pumping oil into the cavity 18 in the bolster 3 which forms the cylinder head. The opposite end of cylinder 17 fits an opening in oil reservoir 19. Tie bolts 20 connect the bolster 3 with the reservoir 19 and serve to draw these elements against the gaskets of cylinders 1'7, 21 and-22, extending between the same. The ends of the cylinders tightly bear against gaskets such as the gaskets 23 and 24 in Fig. 8. V

In order to pump oil from the reservoir 19 tothe cavity 18 and thus operate piston 16, the draft handle 25, Fig. 4, is used to actuate pump operating mechanism. The draft handle is pivoted on a transverse shaft 26 supported in bracket 27 secured to kingpin 5, and therefore may be oscillated in a vertical plane.

The draft handle carries a pawl 28 for engagement with the end of a bell crank lever 29, also journaled on shaft 26. The rounded end 30 of bell crank lever 29 cooperates with the rounded end 31 of a lever 32 which pivots on a shaft 33 carried by bracket arms 341. These arms are integral with the front bolster 4. The lever 32 extends rearwardly of shaft 33 in the form of a fork, Fig.1, which carries a shaft 34. This shaft has a roller 35 on its end for engagement with a plunger 36. The latter reciprocates in a cylindrical guide 37, integral with a cover 38 for the oil reservoir 19. The plunger 36 operates a bell crank lever 39, journaled on the shaft 11. The

lower arm 40 of bell crank 39 carries a roller 41 for engaging the curved head 42 of piston 43.

cylinder 21 fitted in bolster 3. Valves 48 and 50 have ball checks for permitting flow of oil into ghe cavity 51 in bolster 3 and preventing return The operating relationship of this pumping mechanism is best seen in Figure 4. By reason of the fact that the ball heads 30 and 31 contact with each other at a point substantially in line with the axis of the king pin 5, these parts act in the nature of a swiveled connection between the bell crank lever 29 on the steering handle and the'pumping mechanism in the frame; whereby the pumping mechanism may be actuated by the steering handle in any of its steering positions around the king pin 5. Furthermore, by reason of the fact that latch dog 28 and bell crank lever 29 are both mounted on the steering handle, the latching cooperation between these parts is also independent of the steering position of the han dle. Thus regardless'of the steering position of the draft handle, it need merely be swung to a vertical position when the dog 28 will automatically latch with the bell crank lever 29 and the pumping mechanism will be thus instantly available and maybe operated by the operator from.

of pumping pistons.

any position where it is most convenient for him to stand; thus greatly facilitating the utility of the truck for use in crowded places.

The oil level in oil reservoir 19 is above cylinder 21 and therefore this cylinder is filled with oil. Such of the oil that is forced through the check valve 50 is replaced upon return strokes of the piston, by oil flowing from the reservoir 19 through apertures in bearing 44 and collar 46, to an inlet 52 in piston 43, along the passageway 53 in the piston, and through the check valve 48. When the resistance to motion of pistons 43 and 45 is suflicient to prevent these pistons from moving together, spring 47 compresses and piston 43 moves a greater distance than piston 45.

Thus piston 43 by entering the space in the cylinder between piston 45 and the valve 50, displaces less of the oil in this space than if the two pistons were moving together. In either event the pressure produced by the movement of the pistons results 'in forcing oil through the check 50 .into cavity 51 in bolster 3. Cavity 51 communicates by a passageway 54 with the cavity 18 opposite the end of cylinder 17. In this manner piston 16,. Fig. 8, is operated to raise the lift frame 7.

The displacement of the combined pistons 43 and 45 being much greater than that of the piston 43 alone, there will be a rapid movement of the ram piston 16 when the loads are light or when the lifting platform is being lifted into contact with the bottom of a load-supporting skid and when the load is such as to require great pressure, the spring 47 will yield and the piston 43 will then operate as a displacement plunger and will proportionately multiply the power for lifting heavier loads.

To lower the lift frame 7 it is necessary to relieve the pressure against piston 16. This is done by means of a valve 55, Figs. 1, 6 and 7. This valve is located at the end of a tubular conduit 22, which provides a return passageway for oil to the reservoir 19. A tapered valve is preferably employed for this purpose which is carried on the end of an oscillatory shaft 56, operated by a plunger 57, Fig. 5, through the connection 58.

This plunger is shifted against the action of a restoring spring 59 by means of a foot pedal 60. The latter may be held in its depressed position by latch 61.

The valve 55 seats against valve body 62, Fig. 7, and a spring 63 holds the valve to its seat. The spring bears against a screw cap 64 engaging the valve body 62. This cap serves to prevent leakage. When the valve is turned so that its transverse aperture 65 is in alinement with passages 66 and 67 in the valve body 62, oil may flow from the cavity 18, Fig. 1, in bolster 3 to the return conduit 22. The cavity 18 communi cates with cavity 68 through passageway 69.

Trucks of this class are frequently used in connection with load supporting skids such as illustrated in patent to Arthur M. Barrett, No. 1,794,665, Platform, March 3, 1931. Such skids are low platforms having short legs and a truck is pushed beneath the platform between the legs thereof. The draft handle of the truck is gen erally utilized for operating the lifting mechanism which raises the skid and its load from the floor. The draft handle in this instance when vertically oscillated serves to operate a plurality When the load lifted is light enough, all pistons operate in unison, but if the load exceeds some predetermined value,

the heavy duty piston 43, Fig. 4, moves in advance of piston 45, and for each stroke pumps a correspondingly less volume of liquid through the check valve 50 and thus more slowly actuates piston 16, Fig. 8, and its connecting mechanism, with lift frame '7. When the load is light so that piston 45'may move substantially with piston e3, a greater quantity of oil is displaced per stroke of the handle 25 and the load is lifted more rapidly. In such case the pressure developed is insufficient to cause much compression of spring 47.

The lifting frame '7 and its load are lowered by opening valve 55, Fig. 7. The rate of descent is regulated by the flow of oil through this valve. The return of piston 16, Fig. 8, is cushioned by the oil which it forces through the valve.

Although but one specific embodiment of this invention is herein shown and described, it will be understood that certain details of the construction shown may be altered or omittedwithout departing from the spirit of this invention.

I claim:

1. A lift truck comprising a wheeled truck frame having a steering wheel, a horizontally disposed hydraulic ram on said truck frame, means actuated by said ram for lifting a load on said truck, a pump on said frame connected to operate said ram, a handle mounted for pivotal movement in a horizontal plane to control said steering wheel, said handle being also mounted for pivotal movement in a vertical plane, and means coacting with said handle for actuating said pump, said means including vertically movable parts relatively turnable about the axis of horizontal movement of said handle, whereby said handle can operate said pump in various steering positions 2. A lift truck comprising a wheeled truck frame having a steering wheel, a horizontally disposed hydraulic ram on said truck frame, means actuated by said ram for lifting a load on said truck, a pump on said frame connected to operate said ram, a handle mounted for pivotal movement in a horizontal plane to control said steering wheel, said handle being also mounted for pivotal movement in a vertical plane, a lever connected with said pump, and a bell crank pivoted for vertical oscillation by said handle and co-acting with said lever substantial" ly along the line of the axis of horizontal turning of the handle, said bell crank and lever having swiveled relation to each other adjacent said axis of horizontal turning whereby said handle can operate said pump in various steering positions.

3. A lift truck comprising a wheeled truck frame having a steering wheel, a horizontally disposed hydraulic ram on said truck frame, means actuated by said ram for lifting a load on said truck, a pump on said frame connected to operate said ram, a handle mounted for pivotal movement in a horiozntal plane to control said steering wheel, said handle being also mounted for pivotal movement in a vertical plane, a lever connected with said pump, a bellcrank pivoted for vertical oscillation by said handle and co-actmg with said lever substantially along the line of the axis of horizontal turning of the handle, and a latch for connecting said handle and bell-crank, said bell-crank and lever having swiveled relation to each other in the vicinity of the axis of said horizontal turning and all being arranged to permit said handle to operate said pump from various steering positions.

4. A lift truck comprising a wheeled truck frame having a steering wheel, a horizontally disposed hydraulic ram on said truck frame, means actuated by said ram for lifting a load on said truck, a pump on said frame connected to operate said ram, a handle mounted for pivotal movement in a horizontal plane to control said steering wheel, said handle being also mounted for pivotal movement in a vertical plane, a. lever connected with said pump, a bell crank pivoted for vertical oscillation by said handle and co-acting with said lever substantially along the line of the axis of horizontal turning of the handle, said bell-crank having an upstanding arm, and a latch on said handle adapted to engage said upstanding arm to connect saidhandle and bell-crank when said handle is lifted to a certain position, said bell-crank and lever having swiveled relation to each other in the vicinity of the axis of said horizontal turning and all being arranged to permit said handle to operate said pump from various steering positions.

5. A truck of the class described comprising a truck frame structure having supporting whee-ls, an oil reservoir, a transversely extending bolster, three cylinders extending between said bolster and oil reservoir, a lift frame adjustably mounted on said truck frame structure, one of said cylinders being equipped with a pump piston, another of said cylinders being equipped with a piston having lift connections with the lift frame, another of said cylinders being provided with a valve for controlling the return flow of liquid to said reservoir, the bolster ends of all of said cylinders being in communication through cavities and passageways formed in said bolster, a handle swingable about a vertical axis for steering the truck and about a horizontal axis for pumping movements, and mechanism including parts having swiveled relation adjacent said vertical axis and operated through pumping movements of said handle for actuating said pump piston independently of the steering position of said handle.

6. A lift truck, comprising a wheeled truck frame having a steering wheel, a lifting frame on said truck frame, a horizontally disposed hydraulic ram on said truck frame with connections for lifting said lifting frame, pumping mechanism on said truck frame and connected to operate said ram, a handle mounted for pivotal movement in a horizontal plane to control said steering wheel and for pivotal movement in a vertical plane to operate said pumping mechanism, said pumping mechanism including parts having swivel-like relation to each other in the vicinity of the axis of horizontal movement of said handle whereby said handle may operate said pumping mechanism from various positions about said axis.

ARTHUR M. BARRETT. 

